The facet joints can deteriorate or otherwise become injured or diseased, causing lack of support for the spinal column, pain, and/or difficulty in movement.
Facet joint degeneration and disc degeneration frequently occur together, although one may be the primary problem and the other a secondary phenomenon due to altered mechanics of the spine. Central and lateral spine stenosis, degenerative spondylolisthesis, and degenerative scoliosis may all result from the abnormal mechanical relationship between the anterior and posterior column structures of the spine resulting from such joint and/or disc degeneration.
Proper spinal motion requires normal function of both the disc and facet joints. Currently, surgical approaches for spinal stenosis do not restore normal function. In some instances, decompression with removal of soft tissue restraints and portions of the facet joints may actually cause instability, or, at a minimum, alter normal mechanics. As a result, instability that has inadvertently been induced by medical treatment can lead to further degeneration and pain.
Spinal fusion puts stress on adjacent structures, and accelerates transitional degeneration and may cause stenosis at the adjacent segment. Secondary operations for hardware removal are occasionally required, and bone graft donor site pain can be a real problem for many patients.
A flexible facet joint replacement would allow spinal alignment and mobility to be preserved. Also, there would be less stress placed on adjacent levels, and normal anatomic structures (lamina, spinous process, ligaments) could be preserved. Therefore, a need exists for an improved faced joint prosthesis to provide an adjunct to anterior column disc replacement, or as stand-alone treatment for patients with isolated posterior column disease.